HIGH-VELOCITY HOT AMMONIA IN BIPOLAR OUTFLOWS

We have detected high-velocity ammonia emission associated with four bipolar molecular outflows excited by young stars (L1157, L1448, IRAS 3282, and NGC 2071). The high-velocity emission is more prominent in the (3, 3) line, although it is also detected in the (1, 1), (2, 2), and (4, 4) lines. We deduce that the accelerated gas is heated to more than 50-100 K, i.e., a factor of 3-7 over the ambient temperatures (which are in the range 12-26 K). Such temperatures, when taken into account in the analysis of previous SiO observations, confirm that the shocked material is rather dense [n(H-2) approximately 10(5) cm-3]. The NH3 (3, 3) lines, similarly to the SiO emission, arise from shocked material placed along highly-collimated jets or at the lobe ends, and are thus better understood in the frame of jet-driven models for bipolar outflows.